1. Field of the Invention
The present invention relates to a manufacturing method of manufacturing semiconductor light emitting elements by laying a plurality of semiconductor layers one over another on a growth substrate, and particularly to a manufacturing method having a process of separating the growth substrate from the stacked semiconductor layers by laser lift off (LLO).
2. Description of the Related Art
Conventionally, in the field of semiconductor light emitting devices having semiconductor films made mainly of AlxInyGazN (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1), hetero-substrates which are inexpensive allowing of AlInGaN epitaxial growth and on which a semiconductor film of high quality can be crystal-grown have been used for crystal growth. For example, a sapphire substrate is used as the hetero-substrate. However, because the refractive index of the sapphire substrate for blue emission is lower than the refractive index of the semiconductor film, part of blue light emitted from the active layer is reflected back into the active layer, resulting in a decrease in the light extraction efficiency of the semiconductor light emitting device.
In order to solve this problem, in recent years, a so-called vertical type of semiconductor light emitting devices wherein the growth substrate used for the crystal growth of semiconductor films is removed, are attracting attention and are being actively studied. For the removal of the growth substrate, laser lift off (LLO), grinding and polishing, or dry etching is used. For example, Japanese Patent Kokai No. 2006-73619 (Patent Literature 1) and No. 2007-134415 (Patent Literature 2) disclose a method of manufacturing a semiconductor light emitting device using laser lift off.
In the method of manufacturing a semiconductor light emitting device using laser lift-off, separation grooves for releasing N2 gas generated in laser lift-off to the outside of the wafer are usually formed before performing laser lift-off. The separation grooves are formed by dry etching so as to extend through the semiconductor films crystal-grown on the growth substrate and also function as scribe lines. However, because plasma for dry etching damages the semiconductor films, the problem occurs that the side surfaces (exposed through the separation grooves) of a p-clad layer that is one of the semiconductor films become high in resistance and that the side surfaces (exposed through the separation grooves) of the active layer that is one of the semiconductor films lose the light emitting function, resulting in a decrease in the emission power of the semiconductor light emitting device. Further, if impurities scattered during the dry etching and dust having entered in a subsequent process stick to exposed side surfaces of the active layer, the problem occurs that leakage is caused, resulting in a decrease in the yield of semiconductor light emitting elements.
In order to avoid these problems, it is possible to remove the growth substrate without the separation grooves provided (as in, e.g., Reference 2), but cracks will occur in the semiconductor films due to the volume expansion of N2 gas and Ga produced in laser lift-off, resulting in a great decrease in the yield rate of semiconductor light emitting elements.